Method of winding a magnetic core



Nov. 14, 1961 A. G. STEINMAYER METHOD OF WINDING A MAGNETIC CORE 3 Sheets-Sheet 1 I Filed April 23, 1954 ALWIN G. STEINMAYER INVENTOR.

ATTORAE Y Nov. 14, 1961 Filed April 23, 1954 A. G. STEINMAYER METHOD OF WINDING A MAGNETIC CORE 3 Sheets-Sheet 2 INVENTOR. ALWIN G. STEIN MAYER ATTORNEY Nov. 14,- 1961 A. G. STEINMAYER METHOD OF WINDING A MAGNETIC com:

3 Sheets-Sheet 3 Filed April 23, 1954 ALWIN G. STEINMAYER ATTORNEY United States Patent 3,008,222 METHOD OF WINDING A MAGNETIC CORE Alwin G. Steinmayer, Milwaukee, Wis., assignor to Mc- This invention relates to magnetic cores. for stationary induction apparatus and in particular to cores of the wound strip type.

The magnetomotive force required to induce -a given magnetic flux density is a minimum in a core wound from a continuous strip of magnetic material, such as described in Patent No. 2,305,999 to Alwin G. Steinmayer and William E. Krueger assigned to the assignee of this invention. In this type of core, the flux path is uninterrupted.

In installations requiring transformers rated above certain kva. sizes, it is sometimes desirable to use a closed transformer core than can be disassembled-in the field for replacement of the transformer coils. A core that can be disassembled for repair and reassembled thereafter and which performs almost as well as a core of continuous strip is disclosed in the copending application of Oliver G. Attewell, Serial No. 303,232, filed August 8, 1952 and assigned to the assignee of this invention. Atte- Well discloses a core embodying wound larninations of magnetic strip material in which the adjacent ends of successive laminations in the same plane have a length two or three times the width of the magnetic material, thus greatly reducing the flux density across the joint between adjacent ends and increasing the efliciency of the core. The result is a core with performance characteristics superior to other cores embodying butt join-ts between adjacent ends of successive strips.

The diagonal butt joints may be provided in one or both legs of the core and may be arranged to produce a core comprising two U-shaped portions with the core joints being a series of staggered butt joints between ends of the core laminae. The joints in adjacent laminations in the same leg can be crossed or they can be parallel but spaced apart peripherally of the core. The reluctance is minimized if each joint between successive laminations is contiguous uncut portions of laminations in adjacent layers. One method of constructing such a core is by spirally winding a continuous strip of magnetic material, radially cutting through at least one leg of the core along a diagonal, and manually reassembling and restacking the laminations with the joints offset from joints in adjoining laminations.

However, restacking a core in a different pattern from that in which it was originally wound involves problems of fitting and nesting successive laminations since opposed sides of the same convolutions are of unequal length. When the laminations are restacked to dispose the joints in adjacent convolutions in offset relation, some deformation of the core results. This can be rectified to some extent 'by hand stacking, but such procedure is expensive and the results are not entirely satisfactory.

It is the principal object of the invention to provide a method of constructing a magnetic core by winding strips of magnetic material successively, with their adjacent ends substantially abutting each other and out of register with the abutting ends of the strips in adjacent convolutions, into a compactly nested laminated body.

It is further an object of the invention to provide a method of constructing such a magnetic core which is susceptible of disassembly from and reasembly to an electrical coil, which method does not require manual restacking of the magnetic strips in a different pattern from which they were wound to position the abutting ends of successive strips out of register with the abutting ends of successive strips in adjoining convolutions.

Another object of the invention is to provide a method of forming a magnetic core wherein a continuous length of magnetic material is guided toward the core being formed and is sheared into progressively increasing lengths simultaneously with the winding operation.

It is also an object of the invention to provide a method of constructing a magnetic core comprising two U-shaped portions each of which embodies nested strips of magnetic material having their respective ends in substantial butt contact with the ends of corresponding strips in the other portion of the core and preferably spaced peripherally of the core relative to the ends of the strips in adjacent layers. It is a further object to provide such a method of core construction which does not result in deformation of the core and in which the ends of successive strips in the opposed core portions inherently match without the necessity of manual restacking.

An object of one embodiment of the invention is to provide a method of forming a closed core built up of successively abutting strips in spirally nested relation, said method including the steps of winding a continuous strip of magnetic material to preform a closed core of predeternrined peripheral outline, annealing the preformed core, unwinding the preformed core from its inner periphery, shearing the strip into separate strip elements of progressively increasing length, and rewinding the sheared strips elements into a closed core of closely nested convolutions.

Further objects and advantages of the invention will become apparent from the following description referring to the accompanying drawings, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of the specification.

In the drawing:

FIG. 1 is a diagrammatic illustration of the preferred method of forming a core;

FIG. 2 is a fragmentary side view of a preformed core as it is being unwound during rewinding operations;

FIG. 3 is a diagrammatic illustration of a. modified method of forming a core;

FIG. 4 is a plan view illustrating one form of core wound from magnetic strip material by the method herein disclosed, the strip material thickness being exaggerated for a better showing of the core assembly;

FIGS. 5 to 7 are perspective views of alternative cores constructed in accordance with the methods of the invention; and

FIGS. 8a through 8d illustrate in greater detail the portion of the apparatus of FIG. 1 disposed to the right of the shear for automatically feeding the sheared lengths onto the mandrel, and the views show the successive positions of a sheared length of magnetic strip as it is wound on the rotating mandrel.

The initial steps in the practice of the method illustrated in FIGS. 1 and 2 are the winding of a continuous strip of magnetic material on a mandrel of predetermined peripheral contour, the clamping of the wound core, and the annealing of the core to remove stresses in the material and permanently set it in the desired form. The annealed core 1 is then mounted on a face plate or table 2 having a plurality of clamping devices 3 engaging the exterior periphery of the' core 1 and holding the convolutions of the core in nested relation. If desired, the clamping devices 3 may be utilized to clamp the core during the annealing operation.

The plate 2 with the core 1 clamped to it is mounted for rotation about the pivot axis 4 in the direction indicated by the arrow. As the core and table are rotated, the magnetic strip material 12 is withdrawn from the inside of the preformed core 1. The unwinding can be facilitated by pushing out the inner portion of the spirally wound strip, as indicated in FIG. 2, so that the magnetic strip 12 as it is unwound will be freely withdrawn from the core.

The magnetic strip material 12 as it is withdrawn from core 1 is guided between a series of pairs of guide rollers 5 toward a rotatable mandrel 6 where it is rewound with the magnetic strip material occupying the same relative position in the core as previously occupied in the original winding of core 1. The mandrel 6 is rotated in the same direction as the table 2 as mdicated by the arrow and is properly synchronized therewith so that the magnetic strip material 12 is rewound on the mandrel 6 in the same relation thereto as it occupied in the preformed core 1.

A s-called flying shear 7, shown diagrammatically, 18 disposed along the path of the strip 12 as it passes from the core 1 to the mandrel 6, and is provided with interacting cutting edges 8 pivotally and adjustably mounted respectively at 9 and 9a for cutting the strip alternately at opposite angles if desired. The shearing device 7 can be operated by cam or pneumatic means (not shown) for periodically shearing the magnetic strip material 12 at predetermined spaced intervals. It will be understood that the angle of shear relative to length of the strip will be determined by the relationship of the cutting edges thereto. The operation of the flying shear 7 to provide diagonal butt joints between successive strips in the final core will be discussed in detail hereinafter in relation to FIGS. 4 to 7.

Throughout the entire operation, a degree of slackness in the magnetic strip 12 is allowed in order to avoid introducing stresses in the material after annealing and to retain all of the advantages of preforming. The rewind mandrel 6 is positioned relative to and synchronized with the table 2 so as not to introduce stresses in the strip and further engages the strip so that the preformed corner bends occur in proper relation to the corners of the mandrel 6.

Preferably the rollers have a radius no greater than the inner corner radii of the preformed core, thereby avoiding stress at the corner bends of the strip as they pass between the rollers. The rollers should be operated in synchronism with each other and maintain a rotational speed comparative to the speed of the strip as it is transferred from the core 1 to the rewound core. Belts and pulleys or other suitable means (not shown) may be em ployed for operating the table 2, mandrel 6, shear 7 and rollers 5 to maintain a uniform transfer of the magnetic material from the preformed core to the rewound core. Obviously, a greater number of pairs of rollers will be preferable to guide the strip material after the shearing operation than prior thereto. Although I have suggested the use of rollers as guiding means, other means such as a traveling belt or table may be used, especially on the side of the shearing device nearest the mandrel 6.

In order to insure that the severed strips will remain in proper reassembled position on the rewind mandrel 6, a series of pressure rollers 11 are disposed about the mandrel and are yieldingly held in contact with the severed strips by means of springs 10. As illustrated, the rollers 11 are arranged in pairs and are shown disposed at the corners of the mandrel 6 and are preferably pivotally mounted at 13 so that each pair may rock as a unit to conform to the contour of the periphery of the rewound core as the mandrel is rotated. Details of the pressure roller assembly and mounting has not been illustrated since such is well known in the art and in common use in winding cores sold under the trade name of Round-Wound by the assignee of this invention. Other means can be substituted for the rollers, such as a thin continuous insulating strip (not shown) wound with the magnetic material and interposed between adjacent convolutions thereof as the rewinding operation progresses.

FIGS. 8a through 8d show in greater detail the portion of the apparatus of FIG. 1 to the right of the flying shear 7 for feeding the sheared lengths of magnetic strip to and winding them on the core forming mandrel 6 as it is rotated. The sheared lengths 37 of magnetic ribbon have permanently preset corner bends therein which may tend to'move the forward edge of the sheared length 37 in an upward direction between the rollers, and a continuous traveling belt 31 maintained in its path of travel by resilient means acting in a direction against forces tending to cause the sheared lengths 37 to resume the rectangular form in which they were annealed prevents movement of the leading edge of the sheared lengths between the rollers. As shown in FIG. 8a, the continuous belt 31 is maintained in its path of travel by rollers 32 which are rotatably mounted in fixed position and also by rollers 33 which are resiliently urged by springs 34 in a direction opposite to that in which the annealed sheared lengths 37 tend to move. Some of the rollers 32 and 33 may be idler rollers, but at least certain of the rollers 32 and 33 are rotatably driven and frictionally impel the continuous belt 31. The belt 31 in turn frictionally engages the sheared magnetic strip lengths 37 and urges them past a stationary guide 36 to a point adjacent the mandrel 6.

It will be noted in FIG. 8a that a sheared length 37 has been impelled by the belt 31 to a point midway of a longer side 38 of the rectangular core forming mandrel 6. FIGS. 8a through 8d show sequential positions of the mandrel 6, each successive view showing the mandrel 6 rotated forty-five degrees from the preceding position, and illustrate how a sheared length 37 is conducted to and wound onto the mandrel 6.

In FIG. 8b it will be noted that mandrel 6 has rotated forty-five degrees from FIG. 8a to a position where the longer side 38 is substantially parallel to the direction in which the sheared length 37 is fed and further that the leading edge of the sheared length 37 has been urged beneath a roller 11. In FIG. 80 it will be noted that, after forty-five degree further rotation of mandrel 6, a permanently preset bend 39 in the sheared length 37 has assumed its final position against a corner 40 of the mandrel 6 and that the spring urged rollers 11 hold the sheared length 37 against mandrel 6. It will be apparent that the rollers 11 urging sheared length 37 against the mandrel 6 with the corner bend 39 engaging the corner 40 of the mandrel 6 will cause the trailing portion of the sheared length 37 to be pulled around with the mandrel 6. In FIG. 8d the mandrel 6 has rotated until the leading edge of the sheared length 37 is beneath another one of the sets of rollers 11 and a second permanently preset bend 41 in the sheared length 37 has assumed its final position in conformity with a corner 42 of the mandrel 6.

The modified method illustrated in FIG. 3 is similar to that suggested in FIG. 1 but does not require that the core be preformed and annealed prior to the shearing and rewinding operations. In this modification, the strip of magnetic material is withdrawn directly from a rotatably mounted spirally wound reel of the material 15, passed through the flying shear 16 and cut in desired lengths, and then guided to the mandrel l7 and wound thereon in conformity with the contour of the mandrel. The pressure rollers 18, similar to pressure rollers 11 in FIG. 1, should bear against the strip material with sufficient force to shape the strip at the corners of the mandrel and to retain succeeding convolutions in firmly nested relation. After the core has been formed by this modified method, it is then annealed and ready for assembly with an electrical coil.

There is one advantage in this modified method, namely, the guiding rollers 19 may be of larger diameter than those used in the method illustrated in FIG. 1, since they will contact surfaces which have no relatively sharp bends. The modified method also simplifies the guiding of the successively increasing lengths of cut strips and does not require exact rotational synchronism between the reel and mandrel 17. That is, the reel may be allowed some freedom of movement under the retarding effect of mechanism not shown, such as a brake. Of course, the speed of the rollers 19 will be controlled to maintain a definite ratio to the speed of rotation of the mandrel 17.

FIG. 4 represents a completed core and illustrates the manner in which the adjacent ends of succeeding laminations are in abutting relation and in which the laminations are in closely nested relation in successive convolutions. As shown, each convolution comprises two lengths of strip material abutting each other at one end and overlapped at the other ends to oflset the abutting ends in succeeding convolutions peripherally of the core.

The word ofiset and the phrase out of register are used interchangeably throughout the specification and the appended claims to connote the disposal of the butt joints between successive strips so that the flux can transfer to magnetic strips inadjoining convolutions along substantially the entire length of the joint, and it is intended to cover the core embodiments wherein the butt joints in adjoining lamina-tions are spaced peripherally as well as where diagonal butt joints in adjacent convolutions are crossed. To be more technically correct, olfset and out of register connote that the successive cuts are arranged in noncoincident radial planes in a given leg of the final core.

The methods of the invention are particularly suited to construct the core of the aforementioned Attewell application having long diagonal butt joints between'successive strips. The core of FIG. 4 is not limited to long diagonal joints but rather illustrates that the methods of the invention are applicable to any core having butt joints between successive magnetic strips.

To construct the core of FIG. 5 with long diagonal joints 25 parallel to but spaced peripherally of like butt joints in adjoining larninations, the flying shear 7 may be operated to make all cuts at the same angle, but the distance between .cuts is predetermined according to the requirements of the desired arrangement of the butt joints.

If it is desired to have diagonal butt joints between successive strips in one leg only of the core and to have the diagonal joints in adjacent laminations in intersecting relation as shown schematically in FIG. 6, the flying shear 7 may be operated by mechanism (not shown) to cut the magnetic ribbon 12 alternately at opposite angles intothfull length turns '26 of progressively increasing leng If it is desired to have diagonal butt joints in both legs of the core with the joints extending in opposite directions in adjacent laminations in each leg as shown in the coreconstruction of FIG. 7, the flying shear may be operated to cut the magnetic strip 12 into half turn lengths 28 of progressively increasing length with the cutting edges operating twice at one angle and then pivoting to shear the magnetic strip twice at the opposite angle. Such a core comprises two U-shaped portions 29 and 30 with the core joints being a series of staggered izntt joints between ends of the successive strip lengths Although I have shown only a few alternative cores constructed by the methods herein disclosed, it will be obvious to those skilled in the art that such methods be used to form cores of different configuration than illustrated in FIGS. 4 to 7, for example, the ends of each lamination may terminate in the yoke portions of the core rather than in the legs thereof or the magnetic strip may be sheared in two turn lengths to provide butt joints in alternate convolutions only.

It is to be understood that diagrammatic illustration of the manner of practicing the method herein disclosed is merely schematic. Obvious modification will be apparent to those skilled in the art. The end product of my method is the formation of a closed magnetic core comprising a series of successively nested strips of magnetic material into a compact entity with substantially no disturbance in the characteristics of the material. The corners and sides of the laminations fit one upon the other in closely nested relation without bulging sides or ill fitting corners. It is not necessary to apply excessive force to the strips of such magnitude as to introduce stress in the annealed magnetic material.

Heretofore, cores comprising strips of magnetic material disposed successively about the peripheral confines of the core in spiral relation thereto have been assembled by hand through the window of an induction winding. This practice is not only expensive and ineflicient, but requires considerable flexing of the material tending to introduce stress in the material and also makes it somewhat difiicult to match the ends of successive strips in abutting relation. With this prior art method of construction a closely compacted nesting of convolutions could not be obtained with the result that flux transfer between successive convolutions was more or less concentrated in isolated areas of the core. The method herein disclosed removes all of these undesirable results by reason of the precision assembly of the component parts of the core and retains substantially all of the efiiciency of a continuous strip wound core made in accordance with the teachings of the aforesaid Patent 2,305,999 and embodies the desirable characteristics of cores assembled from strips of material disposed successively in a spiral path within the peripheral outlines of the core.

What is cla'r'ned is:

1. The method of forming a closed magnetic core for stationary induction apparatus comprising the steps of winding continuous magnetic strip in successive convolutions into a windowed core of four-sided configuration, holding said core in said four-sided configuration, annealing the core while so held to permanently preset said magnetic strip with comer bends therein, withdrawing the continuous strip from the window side of the core, shearing the strip as it is withdrawn into individual predetermined lengths each of which includes at least two of said corner bends, and rewinding the sheared lengths of magnetic material successively in coplanar relation to reform said core with said lengths in the same relative positions occupied prior to the withdrawing operation and with said preset corner bends inradially' nested relation at the corners of said core.

2. The method of forming a closed magnetic core for induction apparatus, said method comprising the steps of winding a continuous strip of magnetic material in successive convolutions into a windowed core of four-sided configuration, holding said core in said four-sided configuration, annealing the core while so held to permanently preset said magnetic strip with corner bends therein, withdrawing the continuous strip from the window side of the core, shearing the strip as it is withdrawn into successively longer individual predetermined lengths, each of which includes at least two of said corner bends, and rewinding the sheared lengths of magnetic material succasively in coplanar relation to reform said core with said lengths in the same relative positions occupied prior to the withdrawing operation and with said preset corner bends in radially nested relation at the corners of said closed core and with the abutting ends of successive lengths out of register with abutting ends of successive lengths in adjoining convolutions.

3. The method of forming a closed magnetic core for induction apparatus, said method comprising the steps of winding a continuous strip of magnetic material in successive convolutions into a windowed core of four-sided configuration, holding said core in said four-sided configuration, annealing the core while so held to permanently preset said magnetic strip with corner bends therein, withdrawing the continuous strip from the window side of the core, shearing the strip as it is withdrawn into individual predetermined lengths on a line angularly relative to its edges to provide relatively long biased ends on each length and so that each length includw at least two of said corner bends, and rewinding the sheared lengths of magnetic material successively in coplanar relation to reform said core with said lengths in the same relative positions occupied prior to the withdrawing operation and with said preset corner bends in radially nested relation at the corners of said closed core and with the butt joints between successive lengths arranged in noncoincident radial planes in a given leg of the core.

4. The method of forming a closed magnetic core for induction apparatus, said method comprising the steps of winding a continuous strip of magnetic material in successive convolutions on a first four-sided mandrel to form a windowed core, annealing the core thus formed to permanently preset said magnetic strip with bends corresponding to the corners of said four-sided mandrel, withdrawing the continuous strip from the winding side of the core, shearing the strip into successively longer individual predetermined lengths each including at least two of said corner bends on a line angularly relative to its edges as it is withdrawn to provide relatively long biased ends on each length, feeding 'said lengths to a second four-sided mandrel similar to said first mandrel, rotating said second mandrel and rewinding the sheared lengths of magnetic material successively in coplanar relation on said second mandrel to reform said core with said bends in radially nested relation to the comers of said second mandrel and with said lengths in the same relative positions occupied prior to the withdrawing operation and concurrently holding said wound lengths, at spaced positions about the periphery of said second mandrel, in compactly nested relation to the contour of said second mandrel.

5. The method of forming a closed magnetic core for induction apparatus, said method comprising the steps of winding a continuous strip of magnetic material in successive convolutions into a windowed core of foursided configuration, holding said core in said four-sided configuration, annealing the core while so held to permanently preset said magnetic strip with corner bends therein, withdrawing the continuous strip from the window side of the core, shearing the continuous strip into individual predetermined lengths on lines angularly relative to its edges and alternately extending in opposite directions as the strip is withdrawn to provide biased ends in each length angularly relative to each other, and rewinding the sheared lengths of magnetic material successively in coplanar relation to reform said core with said lengths in the same relative positions occupied prior to the withdrawing operation and with said corner bend in radially nested relation at the corners of said closed core, said lengths being such that the abutting ends of successive lengths are out of register with abutting ends of successive strips in adjoining convolutions and each of said lengths includes at least two of said corner bends.

6. The method of forming a closed magnetic core for induction apparatus, said method comprising the steps of winding a continuous strip of magnetic material in successive convolutions into a windowed core four-sided configuration, holding said core in said four-sided configuration, annealing the core while so held to permanently preset said magnetic strip with corner bends therein, withdrawing the continuous strip from the window side of the core, shearing the continuous strip into successively longer individual predetermined lengths on lines angularly relative to its edges and alternately extending in opposite directions as the strip is withdrawn to provide biased ends in each length angularly relative to each other, each of said lengths including at least two of said corner bends, and rewinding the sheared lengths of magnetic material successively in coplanar relation to reform said core with said lengths in the same relative positions occupied prior to the withdrawing operation and with said corner bends in radially nested relation at the corners of said closed core, said predetermined lengths being such that the joints between abutting biased ends of successive lengths are crossed in adjoining convolutions.

7. The method of forming a closed magnetic core comprising the steps of winding continuous magnetic strip in successive convolutions into a windowed core of foursided configuration, holding said core in said four-sided configuration, annealing the core while so held to permanently preset said magnetic strip with corner bends therein, withdrawing the continuous strip from the window side of the core; guiding said strip through a shearing device, operating said shearing device at predetermined intervals as said strip passes therethrough to provide successive lengths of said strip each of which includes at least two of said corner bends, guiding said lengths in coplanar from said shearing device in the order of their succession to a four-sided core forming mandrel having the contour of the window in said core, rotating said mandrel and winding said lengths on said mandrel in said successive order and concurrently resiliently urging said wound lengths at spaced apart points about the periphery of said mandrel into conformity with said mandrel.

8. The method of forming a closed magnetic core for induction apparatus, said method comprising winding a continuous strip of magnetic material in successively nested convolutions on a four-sided mandrel to form a windowed core, annealing the core thus formed to permanently preset said magnetic strip with bends corresponding to the corners of said mandrel; withdrawing the continuous strip from the window side of the core thus annealed and shearing the strip into successively longer individual predetermined lengths each of which includes at least two of said corner bends as it is withdrawn and rewinding the sheared lengths of magnetic strip successively in coplanar relationship to reform said core with said lengths in the same relative positions occupied prior to the withdrawing operation and with the permanently preset bends in radially nested relation at the corners of said reformed core, said predetermined lengths being such that the radial planes of the joints between abutting ends of successive lengths are noncoincident with the radial planes of joints between abutting ends of successive lengths in adjoining convolutions,

References Cited in the file of this patent UNITED STATES PATENTS 789,707 Bellamy May 16, 1905 941,33l Mueller Nov. 23, 1909 1,482,591 Thordarson Feb. 5, 1924 2,245,180 Boyajian June 10, 1941 2,324,115 Schultz July 13, 1943 2,456,457 Someville Dec. 14, 1948 2,467,867 Somerville Apr. 19, 1949 2,542,806 Ford et al. Feb. 20, 1951 2,657,456 Moody Nov. 3, 1953 2,840,889 Freegard July 1, 1958 UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,@08,222 November 14, 1961 Alwin Ga Steinmayer It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read as "corrected belowa Column 8, line 24, after "coplanar" insert form Signed and sealed this 29th day of May l962 (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

